There is known, as a type of a construction machine such as a hydraulic excavator, a hybrid construction machine configured such that an engine is miniaturized to reduce fuel consumption, a generator motor (an assist motor) is connected to the engine to make up a transitional or steady shortfall in output power, and an electric storage device is charged using the output power of the engine, while powering assist is given to drive a hydraulic pump using electric power of the electric storage device. Patent Document 1 describes one example of the hybrid construction machine.
Patent Document 1 proposes exercising control such that a powering assist amount is limited and pump absorption horsepower is limited to prevent the electric storage device from turning into an overdischarge state when an operating state is in a work mode and a remaining charge amount of the electric storage device falls. In other words, a total value of powering output power of a generator motor determined from preset discharge electric energy for a degree of reduction of a charge amount of the electric storage device and output power of an engine is set as an upper limiting value of the pump absorption horsepower, and output power control is exercised such that maximum output power (or torque) from a hydraulic pump is limited to prevent the maximum output power (or torque) from exceeding the value.